Method of forming an interconnect structure of a semiconductor device

ABSTRACT

A structure and a formation method of a semiconductor device structure are provided. The semiconductor device structure includes a semiconductor substrate and a conductive feature over the semiconductor substrate. The semiconductor device structure also includes a dielectric layer over the conductive feature and the semiconductor substrate and a via hole in the dielectric layer. The via hole has an oval cross section. The semiconductor device structure further includes a trench in the dielectric layer, and the via hole extends from a bottom portion of the trench. The trench has a trench width wider than a hole width of the via hole. In addition, the semiconductor device structure includes one or more conductive materials filling the via hole and the trench and electrically connected to the conductive feature.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No. 15/888,906 filed Feb. 5, 2018, which is a divisional application of U.S. application Ser. No. 14/469,059 filed Aug. 26, 2014 and issued as U.S. Pat. No. 9,887,126, the entire disclosures of which are incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while feature size (i.e., the smallest component that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs.

One method used by the industry to meet the demands for device density is the adoption of damascene and dual-damascene structures for interconnect structures. In a damascene process, an underlying insulating layer is patterned with open trenches. Afterwards, a conductor is deposited and polished to the level of the insulating layer to form a patterned conductor feature. Dual-damascene processes use a similar approach and form and fill two features (a trench and a via hole) with a single deposition of conductor.

However, as the feature sizes shrink further and density requirements increase, the pitch between features, such as interconnect structures, decreases. As a result, fabrication processes continue to become more difficult to perform. It is a challenge to form interconnect structures with shorter and shorter pitches in a semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. IL should be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1 to 1J-1 are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 1A-2 to 1J-2 are top views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 2 is a top view of a stage of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 3 is a top view of a stage of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 4 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 5A is a top view of a semiconductor device structure, in accordance with some embodiments.

FIG. 5B is a top view of a semiconductor device structure, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Some embodiments of the disclosure are described. FIGS. 1A-1 to 1J-1 are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. FIGS. 1A-2 to 1J-2 are top views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, the cross-sectional views in FIGS. 1A-1 to 1J-1 are taken along the line I-I of the top views shown in FIGS. 1A-2 to 1J-2.

As shown in FIG. 1A-1, a semiconductor substrate 100 is provided. In some embodiments, the semiconductor substrate 100 is a bulk semiconductor substrate, such as a semiconductor wafer. For example, the semiconductor substrate 100 includes silicon or other elementary semiconductor materials such as germanium. In some other embodiments, the semiconductor substrate 100 includes a compound semiconductor. The compound semiconductor may include silicon carbide, gallium arsenide, indium arsenide, indium phosphide, another suitable compound semiconductor, or a combination thereof. In some embodiments, the semiconductor substrate 100 includes a semiconductor-on-insulator (SOI) substrate. The SOI substrate may be fabricated using a separation by implantation of oxygen (SIMOX) process, a wafer bonding process, another applicable method, or a combination thereof.

In some embodiments, isolation features (not shown) are formed in the semiconductor substrate 100 to define and isolate various device elements (not shown) formed in the semiconductor substrate 100. The isolation features include, for example, trench isolation (STI) features or local oxidation of silicon (LOCOS) features.

Examples of the various device elements, that may be formed in the semiconductor substrate 100, include transistors (e.g., metal oxide semiconductor field effect transistors (MOSFET), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJT), high voltage transistors, high frequency transistors, p-channel and/or n channel field effect transistors (PFETs/NFETs), etc.), diodes, another suitable element, or a combination thereof. Various processes are performed to form the various device elements, such as deposition, etching, implantation, photolithography, annealing, planarization, another applicable process, or a combination thereof.

As shown in FIG. 1A-1, conductive features 102 a and 102 b are formed over the semiconductor substrate 100. In some embodiments, each of the conductive features 102 a and 102 b is a conductive line electrically connected to a corresponding device element. For example, conductive contacts (not shown) are used to form electrical connections between the device elements and the conductive features.

In some embodiments, the conductive features 102 a and 102 b are made of copper, aluminum, gold, titanium, cobalt, tungsten, another suitable conductive material, or a combination thereof. Each of the conductive features 102 a and 102 b has a line width W₁. In some embodiments, the line width W₁ is in a range from about 7 nm to about 20 nm. In some embodiments, the line width W₁ is a minimum line width of conductive lines in the semiconductor device structure. In some embodiments, a pitch P between the conductive features 102 a and 102 b is substantially two times of the line width W₁. The pitch P may be in a range from about 14 nm to about 40 nm.

In some other embodiments, each of the conductive features 102 a and 102 b includes one or more conductive lines and one or more conductive vias. FIG. 1A-1 is a simplified diagram of these cases. The width W₁ represents the line width of the widest conductive line of the conductive feature 102 a or 102 b.

In some embodiments, an insulating layer 104 is formed over the semiconductor substrate 100, as shown in FIG. 1A-1. In some embodiments, the insulating layer 104 is made of silicon oxide, borosilicate glass (BSG), phosphoric silicate glass (PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass (FSG), porous dielectric material, another suitable low-k dielectric material, or a combination thereof. Various processes, including deposition, etching, planarization, or the like, may be used to form the conductive features 102 a and 102 b and the insulating layer 104.

As shown in FIG. 1A-1, an etch stop layer 106 is deposited over the insulating layer 104 and the conductive features 102 a and 102 b, in accordance with some embodiments. The etch stop layer 106 is used to protect the conductive features 102 a and 102 b from being damaged during subsequent processes for forming via holes and trenches. In some embodiments, the etch stop layer 106 is made of silicon carbide (SiC), silicon carbo-nitride (SiCN), silicon oxycarbide (SiCO), silicon nitride (SiN), silicon oxynitride (SiON), another suitable material, or a combination thereof. In some embodiments, the etch stop layer 106 is deposited using a chemical vapor deposition (CVD) process, a spin-on process, another applicable process, or a combination thereof. Embodiments of the disclosure have many variations. In some other embodiments, the etch stop layer 106 is not formed.

As shown in FIG. 1A-1, a dielectric layer 108 is deposited over the etch stop layer 106, in accordance with some embodiments. The dielectric layer 108 serves as an inter-metal dielectric (IMD) layer. In some embodiments, the dielectric layer 108 is made of a low-k dielectric material. The low-k dielectric material has a dielectric constant smaller than that of silicon dioxide. For example, the low-k dielectric material has a dielectric constant in a range from about 1.2 to about 3.5. As the density of semiconductor devices increases and the size of circuit elements becomes smaller, the resistance capacitance (RC) delay time increasingly dominates circuit performance. Using a low-k dielectric material as the dielectric layer 108 is helpful for reducing the RC delay.

In some embodiments, the dielectric layer 108 includes a spin-on inorganic dielectric, a spin-on organic dielectric, a porous dielectric material, an organic polymer, an organic silica glass, SiOF serious material, a hydrogen silsesquioxane (HSQ) series material, a methyl silsesquioxane (MSQ) series material, a porous organic series material, another suitable material, or a combination thereof. In some embodiments, the dielectric layer 108 includes a material including Si, C, O, or H. For example, the dielectric layer 108 includes SiO₂, SiOC, SiON, SiCOH, SiOCN, or a combination thereof. In some embodiments, the dielectric layer 108 is made of carbon-doped silicon oxide. The carbon-doped silicon oxide may also be referred to as organosilicate glass (OSG) or C-oxide. In some embodiments, the carbon-doped silicon oxide includes methyl silsesquioxane (MSQ), hydrogen silsesquioxane (HSQ), polysilsesquioxane, another suitable material, or a combination thereof. In some embodiments, the dielectric layer 108 includes fluorine-doped silicate glass (FSG) such as fluorine-doped —(O—Si(CH₃)₂—O)—. In some embodiments, the dielectric layer 108 is deposited using a CVD process, a spin-on process, a spray coating process, another applicable process, or a combination thereof.

As shown in FIGS. 1A-1 and 1A-2, a hard mask 110 is formed over the dielectric layer 108, in accordance with some embodiments. The hard mask 110 is used to assist in subsequent etching processes. In some embodiments, the hard mask 110 is made of a metal-containing material. The metal-containing material may include titanium, titanium nitride, tantalum, tantalum nitride, tungsten, another suitable material, or a combination thereof. In some other embodiments, the hard mask 110 is made of silicon nitride, silicon oxynitride, polymeric carbon, graphitic carbon, silicon carbide, titanium oxide, silicon, another suitable material, or a combination thereof. In some embodiments, the hard mask 110 includes multiple stacked layers. The multiple stacked layers may be made of the same material. Alternatively, some of the stacked layers are made of different materials.

As shown in FIGS. 1A-1 and 1A-2, the hard mask 110 is patterned to have one or more trench openings such as trench openings 112 a and 112 b, in accordance with some embodiments. The trench openings 112 a and 112 b are used to assist in the formation of via holes and trenches in the dielectric layer 108 in subsequent processes. For example, the trench openings 112 a and 112 b are configured to define or determine positions and sizes of the via holes and the trenches. In some embodiments, the trench openings 112 a and 112 b extend towards the dielectric layer 108 without completely penetrating through the hard mask 110. The trench openings 112 a and 112 b have bottoms 111 a and 111 b, respectively. In FIG. 1A-2, the bottoms 111 a and 111 b are shown in bold lines for clarity. Because the trench openings 112 a and 112 b do not completely penetrate through the hard mask 110, the dielectric layer 108 can still be protected during subsequent processes. Moisture, chemical residues, or the like produced during the subsequent processes could be blocked from entering the dielectric layer 108. The quality of the dielectric layer 108 is maintained. However, it should be noted that embodiments of the disclosure are not limited to the above-mentioned embodiments. In some other embodiments, the trench openings 112 a and 112 b completely penetrate through the hard mask 110 to expose the dielectric layer 108.

In some embodiments, a hard mask layer is deposited over the dielectric layer 108, followed by being patterned to be the hard mask 110. A patterning process, including a photolithography process and an etching process, is used to form the trench openings 112 a and 112 b. In some other embodiments, the hard mask 110 is patterned using an electron beam writing process, an ion beam writing process, a mask-less photolithography process, a laser beam writing process, another applicable process, or a combination thereof.

As the feature size of the semiconductor device continues to decrease, lithography overlay control is getting harder and harder. For example, the line width W₁ of the conductive feature 102 s or 102 b is decreased to be in a range from about 7 nm to about 20 nm. As mentioned above, the trench openings 112 a and 112 b are configured to define or determine the position and sizes of the via holes. Therefore, the alignment between the trench openings and the underlying conductive features also determines the alignment between the via holes and the conductive features. The alignment would affect electrical qualities of the subsequently formed interconnect structures. If there is a serious misalignment between the trench opening and the conductive feature, the subsequently formed via hole is also negatively affected.

As shown in FIGS. 1A-1 and 1A-2, each of the trench openings 112 a and 112 b has a width W₂. In order to ensure an appropriate alignment between the trench opening and the conductive feature, the width W₂ is set to be smaller than the line width W₁, in accordance with some embodiments. Each of the trench opening 112 a and 112 b is positioned right above the corresponding conductive feature 102 a or 102 b. In other words, an imaginary projection of the trench opening on the corresponding conductive feature is positioned between opposite edges of the conductive feature. The imaginary projection does not extend across edges of the conductive feature.

In some embodiments, the width W₂ is in a range from about 5 nm to about 18 nm. In some embodiments, the ratio of the widths W₂ to W₁ (W₂/W₁) is in a range from about 0.5 to about 0.8. Each of the trench openings 112 a and 112 b could be aligned with the conductive feature 102 a or 102 b more easily since the conductive feature is a relatively wide target for the trench opening to aim at.

Even if a misalignment or shifting still occurs during the patterning process for forming the trench openings 112 a and 112 b, the relatively wide conductive feature enables the patterning process of the trench openings to have a larger overlay margin. Each of the trench openings 112 a and 112 b may still be positioned right above the corresponding conductive feature.

In some cases, if the width ratio (W₂/W₁) is higher than about 0.8, the width W₂ might be too large, such that the alignment between the trench opening and the conductive feature is not easy to achieve. In some other cases, if the width ratio (W₂/W₁) is smaller than about 0.5, the width W₂ might be too small, such that the subsequently formed via hole in the dielectric layer 108 has a corresponding small width. As a result, the contact area between the conductive feature (such as the conductive feature 102 a) and a conductive via which will be formed in the via hole might not be sufficient. A high resistance is therefore formed between the conductive via and the conductive feature.

However, it should be appreciated that the width ratio (W₂/W₁) is not limited to a range from about 0.5 to about 0.8. The width ratio (W₂/W₁) may be in a different range in some other cases. For example, the width ratio (W₂/W₁) is in a range from about 0.4 to about 0.9.

Afterwards, a mask layer 114 is deposited over the hard mask 110, as shown in FIGS. 1B-1 and 1B-2 in accordance with some embodiments. The mask layer 114 fills the trench openings 112 a and 112 b, and is then partially removed using a patterning process to form hole openings including hole openings 116 a and 116 b. In some embodiments, the mask layer 114 is made of a photoresist material or the like. The hole openings 116 a and 116 b expose a portion of the hard mask 110 and portions of the trench openings 112 a and 112 h. The bottoms 111 a and 111 b of the trench openings 112 a and 112 b not covered by the mask layer 114 are also exposed by the hole openings 116 a and 116 b, as shown in FIGS. 1B-1 and 1B-2. The hole openings 116 a and 116 b together with the expose trench openings 112 a and 112 b are used to assist in the formation of the via holes in the dielectric layer 108.

As shown in FIGS. 1B-1 and 1B-2, each of the hole openings 116 a and 116 b has a width W₃. In some embodiments, the width W₃ is set to be greater than the width W₂ of the trench opening 112 a or 112 b. Therefore, it is ensured that the hole openings 116 a and 116 b extend across the trench openings 112 a and 112 b, respectively. As shown in FIGS. 1B-1 and 1B-2, an overlapping portion A₁ between the hole opening 116 a and the trench opening 112 a is formed. Similarly, an overlapping portion A₂ between the hole opening 116 h and the trench opening 112 h is also formed.

The overlapping portions A₁ and A₂ together form a via hole pattern which will be substantially transferred to the dielectric layer 108 to form the via holes. Because the hole opening 116 a extends across the trench opening 112 a, the overlapping portion A₁ has a width that is the same as the width W₂ of the trench opening 112 a. Similarly, the hole opening 116 b also extends across the trench opening 112 b. The overlapping portion A₂ between the hole opening 116 b and the trench opening 112 b has a width substantially equal to the width W₂. Each of the overlapping portions A₁ and A₂, which have substantially the same width, corresponds to a via hole which will be formed in the dielectric layer 108.

In some embodiments, the width W₃ is in a range from about 8 nm to about 45 nm. In some embodiments, the ratio of the widths W₃ to W₂ (W₃/W₂) is in a range from about 1.2 to about 3.5. In some cases, if the width ratio (W₃/W₂) is smaller than about 1.2, the width W₃ of the hole opening 116 a might be too small, which leads to a small overlay margin. If a misalignment occurs, some of the hole openings might not be able to extend across the corresponding trench openings. As a result, some of the overlapping portions may have a width smaller than the width W₂. The via holes formed accordingly would have various widths, which negatively affects the product quality.

In some other cases, if the width ratio (W₃/W₂) is higher than about 3.5, the width W₃ might be too large, such that too much area of the hard mask 110 is exposed. The greater the area of the hard mask 110 that is exposed, the greater the likelihood that the exposed hard mask 110 will be damaged during a subsequent via hole etching process. The hard mask 110 exposed by the hole opening 116 a or 116 b may be damaged or removed to expose the dielectric layer 108 and can no longer protect the underlying dielectric layer 108. As a result, a via hole having an undesired width may be formed.

However, it should be appreciated that the width ratio (W₃/W₂) is not limited to a range from about 1.2 to about 3.5. The width ratio (W₃/W₂) may be in a different range in some other cases. For example, the width ratio (W₃/W₂) is in a range from about 2 to about 5.

In some embodiments, each of the hole openings 116 a and 116 b has a substantially circular top-view shape, as shown in FIG. 1B-2. In other words, when observing the hole openings 116 a and 116 b at a position right above the structure shown in FIG. 1B-1, the peripheries of the hole openings 116 a and 116 b are substantially circular. In other words, each of the hole openings 116 a and 116 b has a substantially circular cross section which is taken along a plane parallel to the main surface of the semiconductor substrate 100. However, embodiments of the disclosure are not limited thereto. The top view or the cross section of the hole openings may have a different shape, such as a square shape, an oval shape, a rectangular shape, a triangular shape, a quadrilateral shape, or another suitable shape.

As shown in FIGS. 1C-1 and 1C-2, the dielectric layer 108 is partially removed to form via holes 118 a and 118 b, in accordance with some embodiments. Through the overlapped portions of the hole openings 116 a and 116 b and the trench openings 112 a and 112 b, the hard mask 110 is etched such that the portion of the hard mask 110 under the overlapped portions is removed to expose the dielectric layer 108. Afterwards, another etchant is used in a via hole etching process to etch the dielectric layer 108. As a result, the via holes 118 a and 118 b are formed. During the via hole etching process, the remaining hard mask 110 protects the dielectric layer 108 from being etched. In some embodiments, both the via holes 118 a and 118 b extend into the etch stop layer 106, as shown in FIGS. 1C-1 and 1C-2.

As mentioned above, the overlapping portions A₁ and A₂ (see FIGS. 1B-2) between the hole opening and the trench opening together form the via hole pattern. The via hole pattern is transferred to the dielectric layer 108 to form the via holes 118 a and 118 b after the via hole etching process. The position and the size of the via hole 118 a are together determined or defined by the patterns of the trench opening 112 a and the hole opening 116 a. Therefore, each of the via holes 118 a and 118 b has substantially the same width which is substantially equal to the width W₂ of the trench opening 112 a or 112 b.

As mentioned above, the trench openings 112 a and 112 b are aligned with the respective conductive features 102 a and 102 b. Therefore, the via holes 118 a and 118 b formed accordingly are also aligned with the conductive features 102 a and 102 b, respectively. Both the size and the position of the via holes 118 a and 118 b can be controlled. In some embodiments, the sizes and the profiles of the via holes 118 a and 118 b are substantially the same.

Due to a corner rounding effect, the via hole 118 a formed in the dielectric layer 108 may not have exactly the same top-view shape or exactly the same cross section as the overlapping portion A₁. In some embodiments, the via hole 118 a has a substantially elliptical or oval top-view shape, as shown in FIG. 1C-2. The via hole 118 a has a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100. Similarly, the via hole 118 b also has a substantially elliptical or oval top-view shape, as shown in FIG. 1C-2 in accordance with some embodiments. The via hole 118 b also has a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100.

In some embodiments, each of the via holes 118 a and 118 b includes a long axis and a short axis oriented perpendicular to the long axis, as shown in FIG. 1C-2. The long axis has a long axis length L₁, and the short axis has a short axis length which is substantially equal to the width W₂ of the trench opening 112 a. In some embodiments, the long axis length L₁ is substantially equal to the width W₃ of the hole opening 116 a that has a circular shape from the top view. In some embodiments, the ratio of the long axis length to the short axis length is substantially equal to the width ratio (W₃/W₂). For example, the ratio of the long axis length to the short axis length is in a range from about 1.2 to about 3.5.

In some embodiments, the via holes 118 a and 118 b are simultaneously formed in the same process. However, embodiments of the disclosure are not limited to the embodiments mentioned above. In some other embodiments, a double patterning process is used to form the via holes 118 a and 118 b. In these cases, the via holes 118 a and 118 b are sequentially formed in different processes.

Embodiments of the disclosure have many advantages. For example, the margin of the patterning process of the mask layer 114 is enlarged. FIG. 2 is a top view of a stage of a process for forming a semiconductor device structure, in accordance with some embodiments. As mentioned above, the mask layer 114 is patterned to form the hole openings 116 a and 116 b using a photolithography process in some embodiments. Due to the dimension shrinkage, a misalignment or shifting of the hole openings 116 a and 116 b might occur in some cases. As shown in FIG. 2, in some embodiments, a hole opening 116 b′ is shifted when compared with the hole opening 116 b shown in FIG. 1C-2.

In some embodiments, even if a misalignment or shifting occurs, the shape and size of the overlapping portion between the trench opening 112 b and the hole opening 116 b′ is still substantially the same. Therefore, a via hole 118 b′ formed accordingly still have substantially the same size and the same shape as those of the via hole 118 a or the via hole 118 b shown in FIG. 1C-2. Because the alignment between the trench opening 112 b and the conductive feature (not shown) has been achieved, the via hole 118 b′ is also aligned with the conductive feature.

As shown in FIG. 2, the via hole 118 b′ also has a substantially oval top-view shape or a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100, in accordance with some embodiments. The via hole 118 b′ also includes a long axis and a short axis oriented perpendicular to the long axis, as shown in FIG. 2. The long axis has a long axis length L₂, and the short axis has a shot axis length which is substantially equal to the width W₂ of the trench opening 112 b. In some embodiments, the long axis length L₂ is substantially equal to the width W₃. In some embodiments, the ratio of the long axis length to the short axis length is in a range from about 1.2 to about 3.5. The shapes and sizes of the via holes 118 a and 118 b′ are substantially the same. Conductive vias which will be formed in the via holes 118 a and 118 b′ could exhibit substantially the same electrical quality.

As shown in FIG. 1C-1, the sidewall of the via hole 118 a is substantially vertical to the top surface of the dielectric layer 108, in accordance with some embodiments. However, embodiments of the disclosure have many variations and are not limited to the embodiments shown in FIG. 1C-1. In some other embodiments, the via hole 118 a has a slanted sidewall. In some embodiments, widths of the via hole 118 a gradually decrease along a direction from the top of the via hole 118 a to the bottom of the via hole 118 a.

Embodiments of the disclosure have many variations. For example, the top view shape or the cross section of the via hole is not limited to being substantially oval. In some embodiments, the via hole has a substantially circular top-view shape or a substantially circular cross section taken along a plane parallel to the main surface of the semiconductor substrate. Through tuning the sizes and shapes of the hole opening and the trench opening, the size and shape of the via hole may be varied according to requirements.

FIG. 3 is a top view of a stage of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, the mask layer 114 has a hole opening 116 a′ which has a substantially oval top-view shape or a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100. The hole opening 116 a′ includes a long axis and a short axis oriented perpendicular to the main axis, as shown in FIG. 3. The long axis has a long axis length W₅. The long axis length W₅ is set to be greater than the width W₂ of the trench opening 112 a to ensure that the hole opening 116 a′ extends across the trench opening 112 a.

The short axis has a short axis length L₃. In some embodiments, the short axis length L₃ is substantially equal to the width W₂ of the trench opening 112 a. An overlapping portion between the trench opening 112 a and the hole opening 116 a′ is formed. After the dielectric layer 108 is etched through the trench opening 112 a and the hole opening 116 a′, the pattern of the overlapping portion is substantially transferred to the dielectric layer 108 to form a via hole 118 a′. The via hole 118 a′ has a substantially circular shape from the top view or a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100, as shown in FIG. 3 in accordance with some embodiments.

By tuning the shape or size of the hole opening 116 a′, the shape or size of the via hole 118 a′ can be varied according to requirements. In some embodiments, the short axis length L₃ is greater than the width W₂ of the trench opening 112 a. In these cases, the via hole 118 a′ has a substantially oval top-view shape or a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate. In some other embodiments, the short axis length L₃ is smaller than the width W₂ of the trench opening 112 a. In these cases, the via hole 118 a′ has a substantially oval top-view shape or a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate.

As shown in FIG. 1D-1, the mask layer 114 is removed, and a protective layer 120 is deposited over the hard mask 110, in accordance with some embodiments. In some embodiments, the mask layer 114 is removed using an ashing process, a striping process, or another applicable process. The protective layer 120 fills the via holes 118 a and 118 b and the trench openings 112 a and 112 b. The protective layer 120 is used to protect the via holes 118 a and 118 h during a subsequent trench etching process. In some embodiments, the protective layer 120 is made of a photoresist material or another suitable material. In some embodiments, the protective layer 120 is deposited using a spin-on process, a CVD process, an atomic layer deposition (ALD) process, another applicable process, or a combination thereof.

As shown in FIGS. 1E-1 and 1E-2, the protective layer 120 is etched back, in accordance with some embodiments. In some embodiments, a dry etching process is used to etch back the protective layer 120. For example, an oxygen-containing plasma is used to etch back the protective layer 120. The protective layer 120 outside of the trench openings 112 a and 112 b and an upper portion of the protective layer 120 within the trench openings 112 a and 1120 b are removed. As shown in FIG. 1E-1, after the etching back process, a top surface 121 of the protective layer 121 is below a surface 109 of the hard mask 110.

In some embodiments, the protective layer 120 is etched back in a process chamber in which the pressure is in a range from about 1.5 mTorr to about 300 mTorr. In some embodiments, a gas or a mixture of gas is used for forming a suitable etchant. The gas or mixture of gas may include O₂, N₂, H₂, CF₄, CHF₃, CH₂F₂, CH₃F, Cl₂, another suitable gas, or a combination thereof. In some embodiments, a top source voltage and a bias voltage are used to assist in the etching back process. The top source voltage may be in a range from about 150V to about 1500V. The bias voltage may be in a range from about 5V to about 1000V. In some other embodiments, the bias voltage is not applied.

As shown in FIGS. 1F-1 and 1F-2, the hard mask 110 is partially removed to form a modified hard mask 110 a, in accordance with some embodiments. The trench openings 112 a and 112 b are enlarged to form openings 122 a and 122 b. In some embodiments, an etching process is used to trim the hard mask 110 and form the modified hard mask 110 a. In some embodiments, the etching process is performed without using a photoresist layer. In some embodiments, the modified hard mask 110 a is formed by isotropically etching the hard mask 110. In some embodiments, an isotropic etching operation is performed to the hard mask 110 to remove a surface portion of the hard mask 110. As a result, the hard mask 110 is thinned to form the modified hard mask 110 a, and the trench openings 112 a and 112 b are enlarged to form the openings 122 a and 122 b.

The trench openings 122 a and 122 b together form a trench pattern which will be substantially transferred to the dielectric layer 108 to form the trenches. As shown in FIGS. 1F-1 and 1F-2, each of the trench openings 122 a and 122 b has a width W₄. In some embodiments, the width W₄ is substantially equal to the line width W₁ of the conductive feature 102 a or 102 b. In some embodiments, the width W₄ is in a range from about 7 nm to about 20 nm. In some other embodiments, the width W₄ is greater than the line width W₁ of the conductive feature 102 a or 102 b. For example, the width W₄ is in a range from about 8 nm to about 22 nm.

In some embodiments, the hard mask 110 is etched in a process chamber in which the pressure is in a range from about 1.5 mTorr to about 300 mTorr. In some embodiments, a gas or a mixture of gas is used for forming a suitable etchant. The gas or mixture of gas may include CF₄, CHF₃, CH₂F₂, CH₃F, Cl₂, O₂, N₂, BCl₃, HBr, another suitable gas, or a combination thereof. In some embodiments, a top source voltage and a bias voltage are used to assist in the etching back process. The top source voltage may be in a range from about 150V to about 1500V. The bias voltage may be in a range from about 5V to about 1000V. In some other embodiments, the bias voltage is not applied.

As shown in FIGS. 1G-1 and 1G-2, the dielectric layer 108 is etched through the enlarged trench openings 122 a and 122 b to form trenches 124 a and 124 b, in accordance with some embodiments. In some embodiments, each of the trenches 124 a and 124 b has a trench width substantially the same as the width W₄ of the enlarged trench openings 122 a or 122 b. In some embodiments, the trench width of the trench 124 a or 124 b is substantially equal to the line width W₁ of the conductive feature 102 a or 102 b. The trench width may be in a range from about 7 nm to about 20 nm. In some embodiments, a pitch P′ between the trenches 124 a and 124 b is substantially equal to the pitch P between the conductive features 102 a and 102 h.

In some embodiments, the trenches 124 a and 124 b are simultaneously formed in the same process. However, embodiments of the disclosure are not limited. In some other embodiments, a double patterning process is used to form the trenches 124 a and 124 b. In these cases, the trenches 124 a and 124 b are formed sequentially in different processes.

Due to the protective layer 120, the via holes 118 a and 118 b are protected from being damaged during the etching process for forming the trenches 124 a and 124 b. Therefore, the profiles and the sizes of the via holes 118 a and 118 b are substantially maintained after the formation of the trenches 124 a and 124 b. A portion of the protective layer 120 may be left in the via holes 118 a and 118 b, as shown in FIGS. 1G-1 and 1G-2.

As shown in FIGS. 1G-1 and 1G-2, the trench 124 a has opposite sidewalls 125 a and 125 b. The sidewalls 125 a and 125 b are laterally spaced from the via hole 118 a by distances d₁ and d₂, respectively. In some embodiments, since the hard mask 110 is isotropically etched, the distance d₁ is substantially equal to the distance d₂. The via hole 118 a is positioned under a middle region of the trench 124 a. Similarly, the via hole 118 b is positioned under a middle region of the trench 124 b.

As shown in FIGS. 1G-1 and 1G-2, the trenches 124 a and 124 b have bottom portions 123 a and 123 b, respectively. The via hole 118 a extends from the bottom portion 123 a of the trench 124 a towards the conductive feature 102 a. Similarly, the via hole 118 b extends from the bottom portion 123 b of the trench 124 b.

Afterwards, the protective layer 120 is removed, and the etch stop layer 106 is partially removed to expose the conductive features 102 a and 102 b, as shown in FIGS. 1H-1 and 1H-2 in accordance with some embodiments. In some embodiments, etching processes are performed to sequentially remove the protective layer 120 and the etch stop layer 106. Each of the etching processes may include a wet etching process, a dry etching process, another applicable process, or a combination thereof.

As shown in FIG. 1H-1, the trenches 124 a and 124 b and the via holes 118 a and 118 b are formed in a single-layered structure (i.e., the dielectric layer 108), in accordance with some embodiments. In other words, the dielectric layer 108 is a single layer. The dielectric layer 108 has a lower portion 107 a, surrounding the via holes 118 a and 118 b, and an upper portion 107 b, surrounding the trenches 124 a and 124 b. In some embodiments, there is no etch stop layer between the portions 107 a and 107 b of the dielectric layer 108. The portions 107 a and 107 b are portions of a single dielectric layer.

Afterwards, one or more conductive materials are deposited to fill the trenches 124 a and 124 b and the via holes 118 a and 118 b. As shown in FIG. 1I-1, a conductive layer 126 is deposited over the modified hard mask 110 a to fill the trenches 124 a and 124 b and the via holes 118 a and 118 b, in accordance with some embodiments. The conductive layer 126 is made of one or more conductive materials. The conductive materials may include copper, aluminum, tungsten, titanium, nickel, gold, platinum, cobalt (Co), another suitable conductive material, or a combination thereof. In some embodiments, the conductive layer 126 is deposited using an electrochemical plating process, an electroless plating process, a PVD process, a CVD process, a spin-on process, another applicable process, or a combination thereof. The conductive layer 126 may be a single layer or have multiple stacked layers. In some embodiments, a seed layer (not shown) is used to assist in the formation of the conductive layer 126.

In some embodiments, before the conductive layer 126 is deposited, a barrier layer (not shown) is formed over the sidewalls and bottoms of the trenches 124 a and 124 b and the via holes 118 a and 118 b. For example, the barrier layer is conformally deposited in the trench openings 124 a and 124 b and the via holes 118 a and 118 b. The barrier layer is used to protect the dielectric layer 108 from diffusion of a metal material from the conductive layer 126 sequentially formed. In some embodiments, the barrier layer is made of tantalum nitride, titanium nitride, tungsten nitride, another suitable material, or a combination thereof. In some embodiments, the barrier layer is deposited using a PVD process, a CVD process, another applicable process, or a combination thereof.

As shown in FIGS. 1J-1 and 1J-2, a planarization process is performed to thin down the conductive layer 126 until the dielectric layer 108 is exposed, in accordance with some embodiments. As a result, interconnect structures (or dual damascene structures) of the semiconductor device structure are formed. The interconnect structures include conductive vias 130 a and 130 b and conductive lines 128 a and 128 b. In some embodiments, the planarization process includes a chemical mechanical polishing (CMP) process, a mechanical grinding process, an etching process, another applicable process, or a combination thereof.

Embodiments of the disclosure have many advantages. As shown in FIGS. 1J-1 and 1J-2, the conductive feature 102 a is wider than the conductive via 130 a. The conductive via 130 a is confined by the trench opening 112 a to be positioned right above the conductive feature 102 a. Short circuiting issues are prevented. The conductive lines 128 a and 128 b and the conductive vias 130 a and 130 b are self-aligned with each other, respectively. Each of the conductive vias 130 a and 130 b is positioned under a middle region of the corresponding conductive lines 128 a or 128 b. The size, profile, and shape of the conductive structures formed by the conductive vias 130 a and 130 b and the conductive lines are substantially the same, which results in substantially the same electrical quality. It may not be necessary to form additional circuits to compensate the variations between conductive structures caused by the misalignment or shifting of patterning processes. The design window is significantly enlarged.

Embodiments of the disclosure have many variations. FIG. 4 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. The semiconductor device structure shown in FIG. 4 is formed by using a method that is similar to that illustrated in FIGS. 1A-1J. By fine tuning the etching condition, the sidewalls of the via holes and/or the trenches may be varied. In some embodiments, the via holes 118 a and 118 b have slanted sidewalls. In some embodiments, the trenches 124 a and 124 b have slanted sidewalls.

In some embodiments, the extending directions of the conductive line 128 a and the conductive feature 102 a are substantially parallel to each other, as shown in FIGS. 1J-1 and 1J-2. However, embodiments of the disclosure are not limited to the embodiments mentioned above. FIG. 5A is a top view of a semiconductor device structure, in accordance with some embodiments. The semiconductor device structure shown in FIG. 5A is formed by using a method similar to that illustrated in FIGS. 1A-1J. For clarity, the dielectric layer 108 is not shown. As shown in FIG. 5A, the extending directions of the conductive line 128 a and the conductive feature 102 a are not parallel to each other. In some embodiments, the extending directions of the conductive line 128 a and the conductive feature 102 a are substantially perpendicular to each other.

In some embodiments, the conductive line 128 a is electrically connected to the conductive feature 102 a through a conductive via formed in the via hole 118 a between the conductive line 128 a and the conductive feature 102 a. In some embodiments, the via hole 118 a has a substantially oval cross section taken along a plane parallel to the main surface of the semiconductor substrate 100. The via hole 118 a has a long axis length L₁′. In some embodiments, the long axis length L₁′ is substantially equal to the line width W₁′ of the conductive feature 102 a. In some other embodiments, the long axis length L₁′ is shorter than the line width W₁′ of the conductive feature 102 a.

Embodiments of the disclosure have many variations. In some other embodiments, the via hole 118 a has a substantially circular cross section taken along a plane parallel to the main surface of the semiconductor substrate 100, as shown in FIG. 5B. The via hole 118 has a width L₁“. In some embodiments, the width L₁” is substantially equal to the line width W₁′ of the conductive feature 102 a. In some other embodiments, the width L₁″ is shorter than the line width W₁′ of the conductive feature 102 a.

Embodiments of mechanisms for forming a semiconductor device structure having dual damascene interconnect structures are provided. A hard mask with trench openings and a mask layer with hole openings are provided over a dielectric layer. Overlapping portions between the hole openings and the trench openings form a via hole pattern, which is transferred to the dielectric layer using a via etching process to form the via holes. The hard mask is further trimmed to enlarge the trench openings to form a trench pattern which is self-aligned with the via hole pattern. The trench pattern is also transferred to the dielectric layer using a trench etching process to form the trenches. The trenches and via holes are filled with a conductive material to form the dual damascene interconnect structures. Each of the dual damascene interconnect structures has substantially the same size, profile, and shapes. The performance and reliability of the semiconductor device structure are greatly improved.

In accordance with some embodiments, a semiconductor device structure is provided. The semiconductor device structure includes a semiconductor substrate and a conductive feature over the semiconductor substrate. The semiconductor device structure also includes a dielectric layer over the conductive feature and the semiconductor substrate and a via hole in the dielectric layer. The via hole has an oval cross section. The semiconductor device structure further includes a trench in the dielectric layer, and the via hole extends from a bottom portion of the trench. The trench has a trench width wider than a hole width of the via hole. In addition, the semiconductor device structure includes one or more conductive materials filling the via hole and the trench and electrically connected to the conductive feature.

In accordance with some embodiments, a semiconductor device structure is provided. The semiconductor device structure includes a semiconductor substrate and a conductive feature over the semiconductor substrate. The conductive feature has a line width. The semiconductor device structure also includes a dielectric layer over the conductive feature and the semiconductor substrate. The semiconductor device structure further includes a via hole in the dielectric layer and a trench in the dielectric layer, and the via hole extends from a bottom portion of the trench. The trench has a trench width wider than a hole width of the via hole and substantially equal to the line width. In addition, the semiconductor device structure includes one or more conductive materials filling the via hole and the trench and electrically connected to the conductive feature.

In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes providing a semiconductor substrate with a conductive feature formed on the semiconductor substrate. The method also includes forming a dielectric layer over the semiconductor substrate and the conductive feature. The method further includes forming a hard mask over the dielectric layer. The hard mask has a trench opening aligned with the conductive feature. In addition, the method includes forming a mask layer over the hard mask. The mask layer has a hole opening extending across the trench opening and exposing a portion of the trench opening. The method also includes etching the dielectric layer through an overlapping portion between the hole opening and the trench opening to form a via hole in the dielectric layer. The method further includes partially removing the hard mask to enlarge the trench opening and etching the dielectric layer through the enlarged trench opening to form a trench in the dielectric layer. In addition, the method includes filling one or more conductive materials in the trench and the via hole.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a semiconductor device structure, comprising: providing a semiconductor substrate with a conductive feature formed thereon, the conductive feature has a first width in a first direction; forming a dielectric layer over the semiconductor substrate and the conductive feature; forming a hard mask over the dielectric layer, wherein the hard mask has a trench opening having a second width in the first direction, the trench opening vertically aligned with the conductive feature; forming a mask layer over the hard mask, wherein the mask layer has a hole opening having a third width in the first direction, wherein the third width is greater than the second width and extends across the trench opening and exposing a portion of the trench opening; while using the hard mask and the mask layer as masking elements, etching the dielectric layer through an overlapping portion between the hole opening and the trench opening to form a via hole in the dielectric layer extending from a surface of the dielectric layer; forming a protective layer in the via hole, wherein the forming the protective layer includes etching back the protective layer such that a top surface of the protective layer is below a top surface of the hard mask; after forming the via hole extending through the dielectric layer, partially removing the hard mask to enlarge the trench opening; etching the dielectric layer through the enlarged trench opening to form a trench in the dielectric layer; and filling at least one conductive material in the trench and the via hole.
 2. The method of claim 1, wherein the forming the protective layer includes depositing photoresist.
 3. The method of claim 1, further comprising: removing the protective layer after the trench is formed and before the filling the at least one conductive material.
 4. The method of claim 1, further comprising removing the mask layer before forming the protective layer.
 5. The method of claim 1, further comprising: depositing an etch stop layer over the conductive feature prior to forming the dielectric layer.
 6. The method of claim 5, wherein the etching the via hole includes etching into the etch stop layer.
 7. The method of claim 1, wherein the forming the hard mask over the dielectric layer includes the trench opening extending to a first depth in the hard mask, the first depth being less than a thickness of the hard mask.
 8. A method for forming a semiconductor device, comprising: providing a semiconductor substrate having a conductive feature disposed thereon; depositing a dielectric layer over the semiconductor substrate and the conductive feature; depositing a hard mask layer over the dielectric layer, wherein the hard mask layer has a first opening over the conductive feature wherein a first portion of a surface of the dielectric layer is exposed in the first opening; forming a mask layer over the hard mask layer, wherein the mask layer has a second opening above the first opening, the second opening vertically aligned with and having a larger horizontal width than the first opening; etching the dielectric layer to form a via hole having a constant width through the dielectric layer; etching the hard mask layer after filling the via hole with a protective material, wherein the etching the hard mask layer enlarges the first opening to provide an enlarged first opening, wherein the mask layer is removed before filling the via hole with the protective material; and etching the dielectric layer through the enlarged first opening.
 9. The method of claim 8, wherein the etching to form the via hole includes forming an oval shaped via hole.
 10. The method of claim 8, further comprising: etching back the protective material prior to partially removing the hard mask layer.
 11. The method of claim 8, wherein the protective material is disposed in the via hole during the etching the dielectric layer through the enlarged first opening.
 12. The method of claim 8, wherein the etching the dielectric layer through the enlarged first opening forms a trench.
 13. The method of claim 12, further comprising: filling the trench and the via hole with a conductive material.
 14. The method of claim 8, further comprising: removing the protective material.
 15. The method of claim 8, further comprising: forming an etch stop layer under the dielectric layer and above the conductive feature, and wherein the etching the via hole through the dielectric layer forms the via hole having a bottom defined by the etch stop layer.
 16. The method of claim 8, wherein the protective material is a photoresist material.
 17. A method of fabricating a semiconductor device structure, comprising: forming a conductive feature over a semiconductor substrate, wherein the conductive feature has a line width and a line length, the line width defined in a first direction and the line length extending in a second direction perpendicular to the first direction; forming an etch stop layer over the conductive feature; depositing a dielectric layer over the conductive feature, the etch stop layer, and the semiconductor substrate; forming a masking element defining a via hole, wherein forming the masking element includes forming a first layer with a first opening and a second layer overlying the first layer with a second opening, wherein an overlap of the first opening and the second opening define the via hole; etching the via hole in the dielectric layer and extending into the etch stop layer while the masking element is disposed over the semiconductor substrate, wherein the etching the via hole provides slanted sidewalls terminating at the conductive feature; after etching the via hole extending into the etch stop layer, removing the second layer of the masking element and maintaining the first layer of the masking element, and etching a trench in the dielectric layer over the via hole, wherein the via hole extends from a bottom portion of the trench, and the trench has a trench width wider than a hole width of the via hole and substantially equal to the line width, wherein the via hole has an oval shaped opening in the bottom portion of the trench; and filling the via hole and the trench with at least one conductive material to electrically connect to the conductive feature, wherein the conductive material filling the trench has the trench width defined in the second direction and a trench length extending in the first direction.
 18. The method of claim 17, wherein the forming the etch stop layer over the conductive feature includes forming the etch stop layer directly on a top surface of the conductive feature.
 19. The method of claim 17 wherein the etching the trench includes etching a rectangular shaped opening having the trench width along a length greater than a length of the via hole.
 20. The method of claim 17, wherein during the etching the trench in the dielectric layer, a protective layer is disposed in the via hole. 